Puree vinegar, capers, 3 tablespoons mustard, and shallots until well blended. Pour into a bowl. Add the remaining mustard around the edge of the bowl and fold into the mixture. Add the oil in a stream while stirring constantly until creamy.
Combine all of the ingredients in a large bowl. Transfer about 1 1/2 cups of the salad mixture into serving bowls. Coat lightly with some dressing and toss to combine. Serve immediately.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.